Composite Particle For Steel Making and Ore Refining

ABSTRACT

Composite particles are used in combination with ore particles in an ore-refining or purification process, such as in a steel- or iron-making process. The composite particles comprise a core, which may be an aggregate of limestone, dolomite, or another ore particle. The core is surrounded by a coating layer of a metal dust and a binder. The metal dust may be iron oxide dust, which, along with limestone, is prevalent in the iron smelting process anyway. In this way, the composite particles help to recycle otherwise wasted and hazardous iron dust. The binder may be mineral clay such as bentonite, montmorillonite or kaolinite, and may comprise about 2-10% by weight of the particle.

BACKGROUND OF THE INVENTION

The present invention relates to improved methods of making steel orother metals using recycled/recovered waste products to make compositeparticles that can be re-used in the metal-making and ore refiningprocesses. Suitably-sized waste products may be employed as cores andwaste fines or dusts may be employed in coatings of the compositeparticle.

Steel is an alloy of iron and carbon that is typically produced in atwo-stage process. In a first “ore-refining” stage, iron ore is reducedor smelted with coke and limestone in a blast furnace, producing molteniron which may be cast into pig iron or carried to the next stage asmolten iron. In the second stage, known as “steelmaking”, impuritiessuch as sulfur, phosphorus, and excess carbon are removed and alloyingelements such as manganese, nickel, chromium and vanadium are added toproduce the exact steel formulation required. Steel mills then turnmolten steel into blooms, ingots, slabs and sheets through casting, hotrolling and/or cold rolling. Other metals and alloys may be made inanalogous processes of “ore refining” and “metal making.”

Byproducts of the iron- and steel-making process depend, in part, on theparticular process used but generally include various slags, sludge anddust. Dust and sludge are collected in the abatement equipment (filters)attached to the iron- and steel-making processes. Sludge is producedfrom dust or fines in various steelmaking and rolling processes and hasa high moisture content. The dust and sludge removed from the gasesconsist primarily of iron and iron oxides and can mostly be used againin steelmaking. Iron oxides that cannot be recycled internally can besold to other industries for various applications, from Portland cementto electric motor cores,

However, iron oxide dust is a hazardous substance when inhaled, andtherefore somewhat dangerous to handle in large quantities. For example,the MSDS for iron oxides states: “May cause irritation to therespiratory tract. Symptoms may include coughing and shortness ofbreath. Long term inhalation exposure to iron has resulted in mottlingof the lungs, a condition referred to siderosis,” OHSA has set a legalairborne permissible exposure limit (PEL) of 10 mg/m³ averaged over an8-hour workshift for iron oxide fumes, and 5 mg/m³ for iron oxide dustor particulates. Consequently, if iron oxides are sold as waste orbyproducts, they generally must be treated as a hazardous substance andspecial precautions are required for transport and storage, adding todisposal costs.

In some steel-making plants, iron fines not suitable for direct use inthe blast furnace are recycled in various ways. For example, inWO1992/007964, a process for recycling ore fines is described whereinthe dust and sludge from the blast furnace and converters is mixed andthe mixture is added to the stream of converter slag when the moltenslag is poured into a ladle. The stream force draws the mixture downinto the molten slag. The resultant slag is solidified, crushed andreintroduced to the blast furnace. Also, Bluescope steel has described arecycle process in which ore fines are mixed with lime fines and coke toagglomerate the fines, followed by sintering in a flame chamber to fusethe fines and coke agglomerate. See, for example:https://www.bluescopesteel.com/media/10538/Reusing%20the%20By-Products1.pdf.

It would therefore be advantageous to find ways to recycle and reuseiron oxide dust and/or other metal dusts or fines without having todispose of them offsite, and without having to further process them bymolten slag, agglomeration or sintering into usable substances.

SUMMARY OF THE INVENTION

The invention relates to composite particles useful for making metalalloys such as iron and steel, the composite particle comprising a coreof an aggregate material and a coating surrounding the core, the coatingcomprising a metal dust such as a iron oxide dust, and a binder.Composite particles so formed may be used like any ordinary ore particlein an ore refining process. Thus, in a first aspect, the inventionrelates to a composite particle comprising:

an aggregate core;

a coating around the aggregate core, the coating comprising metal dustand a binder.

In some embodiments, the metal dust is iron oxide dust and the aggregatecore is a limestone or dolomite particle, or a taconite particle, whichare often used in steelmaking anyway, so they is prevalent in steelmills. The cores may be sized to a standard size number of about 7-10,for example 8 to 9. In some embodiments the binder may comprise mineralclay such as the kaolinite, montmorillonite/smectite/bentonite,palygorskite/attapulgite, vermiculite, and minnesotaite groups. In someembodiments, the binder may comprise from about 2% to about 10% byweight of the composite particle, for example about 5%. Thus, the bulkof the composite particle (e.g. from about 90% to about 98% by weight)is the aggregate and iron dust, which are already components used insteelmaking, In some embodiments the metal (e.g. iron oxide) dust maycomprise about 20% to about 60% by weight of the composite particle,such as from about 30% to about 50% by weight. The coating is relativelythin, so that the final composite particle may have standard size numberfrom 6-9 or 6-8, only slightly larger than the aggregate core. Thecomposite particles may be formed in a batch rolling process as is knownin the art.

In other embodiments, the core may comprise any other ore particle ofsuitable size, and the metal dust may comprise fines or dusts of anymetal useful in making a desired alloy.

In a second aspect, the invention relates a process for making metals oralloys by (1) smelting composite particles described above with othermetal ores; (2) cooling the molten ore-melt; and (3) optionally furtherprocessing the metal with carbon or other elements and to remove furtherimpurities, and optionally alloying it with other metals. In aparticular embodiment, the invention relates a process for making ironand/or steel by (1) smelting composite particles described above havingdolomite or limestone cores and iron oxide dust with other iron ore; (2)cooling the molten pig iron; and (3) optionally further processing thesteel with carbon and to remove further impurities, and optionallyalloying it with other metals.

Other features and advantages of the invention will be apparent from thedetailed description that follows.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to composite particles useful for making iron andsteel, the composite particle comprising a core of an aggregate materialand a coating surrounding the core, the coating comprising iron oxidedust and a hinder. Composite particles so formed may be used like anyordinary ore particle. They also are a means to recycle iron oxidedust—normally a waste byproduct—within in a steel mill.

Those of ordinary skill in the art will realize that the followingdetailed description of the embodiments is illustrative only and notintended to be in any way limiting. Other embodiments will readilysuggest themselves to such skilled persons having the benefit of thisdisclosure. Reference to an “embodiment,” “aspect,” or “example” hereinindicate that the embodiments of the invention so described may includea particular feature, structure, or characteristic, but not everyembodiment necessarily includes the particular feature, structure, orcharacteristic. Further, repeated use of the phrase “in one embodiment”does not necessarily refer to the same embodiment, although it may.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described herein. All references cited herein,including books, journal articles, published U.S. or foreign patentapplications, issued U.S. or foreign patents, and any other references,are each incorporated by reference in their entireties, including alldata, tables, figures, and text presented in the cited references.

Numerical ranges, measurements and parameters used to characterize theinvention—for example, angular degrees, quantities of ingredients,polymer molecular weights, reaction conditions (pH, temperatures, chargelevels, etc.), physical dimensions and so forth—are necessarilyapproximations; and, while reported as precisely as possible, theyinherently contain imprecision derived from their respectivemeasurements. Consequently, all numbers expressing ranges of magnitudesas used in the specification and claims are to be understood as beingmodified in all instances by the term “about.” All numerical ranges areunderstood to include all possible incremental sub-ranges within theouter boundaries of the range. Thus, a range of 30 to 90 unitsdiscloses, for example, 35 to 50 units, 45 to 85 units, and 40 to 80units, etc. Unless otherwise defined, percentages are wt/wt %.

Composite Particles

Composite particles similar to those of the invention are known anddescribed in the art along with various specific embodiments and/orsediment capping systems containing the same. See for reference U.S.Pat. No. 5,538,787, which issued to Nachtman et al. on Jul. 23, 1996,U.S. Pat. No. 5,897,946, which issued to Nachtman et al. on Apr. 27,1999, U.S. Pat. No. 6,386,796, which issued to Hull on May 14, 2002,U.S. Pat. No. 6,558,081, which issued to Hull on May 6, 2003, U.S. Pat.No. 7,011,766, which issued to Hull on Mar. 14, 2006, U.S. Pat. No.7,438,500, which issued to Hull on Oct. 21, 2008, and WO 2012/048215published Apr. 12, 2012, each of which is incorporated herein byreference in their entirety.

The size of the composite particle can range from a small pebble to alarge size rock or even larger. Preferably, the composite particle isgenerally spherical in form, but it can also be other shapes such asoval, egg, oblong, or irregular giving rise to at least one major axisand at least one minor axis. Particles may he sized by reference totheir major dimension, which generally gives rise to an average size.Alternatively and more conveniently, particles may be sized by referenceto the sieve or mesh size which allows them to pass through, thusgenerating a maximum size parameter. The AASHTO uses this latter methodand attributes a standard “size number” to aggregate or particles thathave a particular size distribution as set forth in their Table 1,partially reproduced below. The larger the “size number” the smaller theparticle. For example, aggregate particles of standard size number 8will have a size distribution such that all will pass a 12.5 mm sieve,most (85-100%) will pass a 9.5 mm sieve, only 10-30% will pass a 4.75 mmsieve, etc.

TABLE 1 adapted from AASHTO Standard Sizes of Processed AggregateAggregate size distributions, given as Percent (mass) that passesthrough each standard laboratory sieve 19.0 12.5 9.5 4.75 2.36 1.18AASHTO 25.0 mm mm mm mm mm mm “Size mm (¾ (½ (⅜ (No. (No. (No. Number”(1 in.) in.) in.) in.) 4) 8) 16) 5 90-100 20-55  0-10 0-5  — — — 6 10090-100 20-55  0-15 0-5  — — 7 — 100 90-100 40-70  0-15 0-5 — 8 — — 10085-100 10-30   0-10 0-5  9 — — — 100 85-100 10-40 0-10 10 — — — 10085-100 — —

Composite particles of the invention generally have a major axisdimension of from about ¼ inch to 1 inch or more; more typically fromabout ⅜ inch to about ½ inch. Alternatively, composite particles of theinvention may be sized as are aggregates by the AASHTO standard sizes,and particles having a standard size number from 6 to 9, or from 6 to 8should be suitable.

Cores

The core of the composite particle may be formed of nearly any material,may comprise from about 10 to about 80% of the major axis dimension andfrom about 30 to 80% of the total weight of the composite particle.Cores may also be sized as are aggregates by the AASHTO standard sizes,and size numbers 7 to 10 or from 8 to 9 may be used, correspondinggenerally to major dimensions of about 3/16 to about ½ inch, or from ¼to about ⅜ inch. Cores may comprise a solid stone or rock core such as afine aggregate and/or coarse aggregate. Fine aggregate includes smallparticles such as sand and other sand-sized materials. Coarse aggregateincludes larger particles such as gravel, crushed stone, recycledaggregates (from construction, demolition and excavation waste), andmanufactured aggregates (for example, furnace slag and bottom ash).

A particularly useful core material in steel making plants isappropriately sized limestone or dolomite aggregates. Other useful corematerials—particularly for steel-making—include iron ore or taconitenuggets or pellets. Taconite is a form of low-grade iron ore and it maybe mined from various locations including the Mesabi Iron Range, nearHibbing, Minn. To make these pellets, the hard taconite ore is blastedand then ground down with water to a fine powder. The fine iron-richparticles, mostly of magnetite are extracted from the powder by use ofmagnetism. The wet taconite powder is rolled with clay inside largerotating cylinders. The cylinders cause the powder to roll intomarble-sized halls. The balls are then dried and heated until they arewhite hot. The balls become hard as they cool. The finished product istaconite pellets. Other iron-related minerals that may also be suitableas cores include, for example, Grunerite/Cummingtonite(Mg,Fe)₇Si₈O₂₂(OH)₂; Actinolite Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂; Minnesotaite(Fe,Mg)₃Si₄O₁₀(OH)₂; Greenalite (Fe)₂₋₃Si₂O₅(OH)₄; and StilpnomelaneK(Fe,Mg)₈(Si,Al)₁₂(O,OH)₂₇.n(H₂O).

Also useful as cores are any “steel slag” pellets or fines as that termis used in the industry. During steelmaking (particularly, theopen-hearth method), the addition of limestone or dolomite (calciumcompounds) forms complexes with aluminum, silicon and phosphorus to form“slag”—a waste product of steelmaking. Slag floats to the top of themelt, is poured off and placed in piles for disposal. The slag cools soquickly, in fact, that it solidifies as an amorphous, glass-like solidranging from fine sand particles to large blocks, both of which can beextremely hard. Much of the metallic fraction (the discarded steelproducts in the pile) is removed with large magnets and sold as steelscrap. The resulting nonmetallic grades have applications inconstruction and in the present invention. The finest fractions (aboutNo. 8 or smaller) are referred to as “slag fines”. But properly sizedslag may serve as cores for the invention.

Cores useful for making other metals or alloys include the coresmentioned above, and also ore particles of any ore used in making thedesired metal or alloy.

The core may be more dense, less dense or equally as dense as thecoating layer. In an exemplary embodiment, the core has a relativelygreater density as compared to that of the coating layer.

Coating Layer

The coating layer of the composite particles may partially or completelyencapsulate the core. The coating is made of at least two components:metal dust and a binder. The metal dust is preferably the dust of ametal to be incorporated into the metal or alloy, such as iron oxidedust can be incorporated into the making of steel or iron.

In many embodiments, the binder material is a clay mineral or a mixtureof clay minerals that, while not hardening, does generate cohesivestrength by the hydration process. Clay is common name for a widevariety of weathered mineral or igneous rock. Various classificationschemes, such as the Nickel-Strunz classification, divide up mineralclays according to composition and/or structure. Suitable clays may befound in the kaolinite group, the smectite or montmorillonite group, theattapulgite group and the zeolite group. Generally, these groups containsheets or layers formed of specific tetrahedral and/or octahedralstructures of aluminum and silicon oxides. The layers or platelets areheld together by ionic bonds with charged ions (usually cations) locatedbetween the layers. The Nickel-Strunz classification (version 10)divides silicates (group 9) into nine different subcategories, the mostuseful being Phyllosilicates (group 9E) and the Tektosllicates with andwithout Zeolitic H₂O (groups 9G and GF, respectively). Phyllosilicates(group 9E) are divided into nine subcategories, the most useful beinggroup 9EC (with mica sheets), group 9ED (with kaolin layers), and group9EE (single tetrahedral nets of six-membered rings). Exemplary days fromthese groups include kaolinite, montmorilionite (also called smectiteand bentonite), talc, mondorite, nontronite, palygorskite orattapulgite, muscovite, vermiculite, saponite, hectorite, rectorite, andminnesotaite. Bentonite is a useful impure clay largely containingmontmorillonite.

It is the layers or “platelets” of phyllosilicates that give them manyof their properties, including the plasticity for use as pottery. Whenthe layers are of thickness dimensions in the few nanometer range, theyare often referred to as nanoclays. An example is the NANOLIN DK seriesof nanoclays available from Zhejiang Fenghong Clay Chemicals Co., LTD.,which are made from highly purified smectite that exhibits ultra-finephase dimensions. The size of these nanoclays is typically in the rangeof 1-100 nm; the average fully dispersed thickness of platelets isaround 25 nm; the aspect ratio ranges from 100 to 1000.

Modified clays are formed when various processes are used to separateand expand the layers or platelets. Intercalation, exfoliation, andfuming are processes that modify the layered structure. Intercalationinserts a polymer or other molecule between the platelet layers toisolate them, but without much physical separation. Exfoliation, on theother hand, inserts a polymer or molecule and expands the space betweenlayers by 10-20 fold. Fuming is a flaming process that introduceshydroxyl groups onto the surface of the silica structures.

A clay-sized material can also be used, such as gypsum, flyash, cement,or other materials, having an average particle size of less than about10 microns. The binder material may also include other clay-sized orquasi clay-sized materials such as organophilic bentonite, zeolites, andinorganic oxides of aluminum, iron, and/or manganese.

The binder may be present in the composite particle in amounts fromabout 2% to about 10% by weight, for example, from about 3% to about 7%,or about 5% by weight.

The second component of the coating layer is the metal dust, of whichone embodiment is iron oxide dust. According to the steel industry, ironore is typically crushed to a size of about 7 mm to about 25 mm for usein the blast furnaces, corresponding roughly to a size number of about 5to about 8. Particulates smaller than about 6 or 7 mm in size areconsidered “fines” and are either not used or are re cycled as describedin the background. In contrast, “dust” refers to particles that aresmaller still, having a particle size in the range of about no more thanabout a hundred microns; or a size such that essentially 100% passesthrough a standard No. 150 mesh.

Collection of iron oxide dust generally already takes place in steelmaking plants to avoid dispersing the hazardous dust. Collection bags orfilters may be used, as well as certain types of scrubbers andseparators to isolate the iron oxide dust from other useful componentsthat might he in the process stream (e.g. gases and other particulates).

Other metal dusts that may be useful in the coating include aluminum,copper, nickel, chromium, molybdenum, titanium, zirconium, manganese,magnesium, tungsten, cobalt, zinc, silver, platinum, palladium, gallium,indium, tin, and the like, it will be understood that compositeparticles containing these other metal dusts may be used in metal-makingor alloy-making processes analogous to steelmaking, with the selectionof composite particle core and dust component of the coating beingdependent on the particular metal or alloy to be made.

The metal particle dust may be included in the composite particles inamounts from about 20% to about 60% by weight of the particle, forexample from about 30% to about 50% by weight.

Composite Particle Manufacture and Use

The composite particles of the invention can he manufactured by a batchrolling process, using a roller such as a concrete mixer or pugmill.Typically the binder and iron oxide dust will be combined into a mixturethat is applied as a coating to the core which has been prewetted with awater-based emulsified hinder. The prewetted cores and coating materialsare added to the mixer, and rotation causes the cores to become coated,and compacting of the coating layer on the core may occur as theaggregates fall and collide against the wall of the roller.

Alternatively, the composite particles can be manufacture usingprocesses analogous to those described in the patent literature citedand incorporated herein in connection with composite particles forsedimentation capping systems.

Composite particles are then used in a blast furnace in the same way anaggregate of ore might be used, to smelt into iron, potentially for theultimate production of steel. These processes of using ore are wellknown and need not he described in detail herein. The binder material ofthe coating layer will often vaporize, leaving only the core aggregateand the iron oxide dust—two of the principal components of smelting.

The principle and mode of operation of this invention have beenexplained and illustrated in its preferred embodiments. However, it mustbe understood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

1. A composite particle comprising: a core comprising an aggregate oflimestone, dolomite, or taconite; a coating on the core, the coatingcomprising a metal dust and a binder material.
 2. The composite particleof claim 1, wherein the binder material is selected fromPhyllosilicates.
 3. The composite particle of claim 2, wherein thebinder material is selected from the kaolinite,montmorillonite/smectite/bentonite, palygorskite/attapulgite,vermiculite, and minnesotaite.
 4. The composite particle of claim 1,wherein the binder material is present in an amount from about 2% toabout 10% by weight of the composite particle.
 5. The composite particleof claim 4, wherein the binder material is present at example about 5%.6. The composite particle of claim 1, wherein the metal dust comprisesiron oxide dust.
 7. The composite particle of claim 1, wherein the coreaggregate comprises from about 30 to about 90% by weight of thecomposite particle.
 8. The composite particle of claim 1, wherein thecore is an aggregate sized to a standard size number from about 7-9. 9.The composite particle of claim 6, wherein the iron oxide dust ispresent in an amount from about 20% to about 60% by weight of thecomposite particle.
 10. The composite particle of claim 9, wherein theiron oxide dust is present in an amount from about 30% to about 50% byweight.
 11. The composite particle of claim 1, wherein the compositeparticle is sized to a standard size number from about 6-9.
 12. An ironcomposition comprising coke, ore and a plurality of composite particlesaccording to claim
 6. 13. A steel manufactured from iron made usingcomposite particles according to claim
 6. 14. The composite particle ofclaim 1, wherein the core is a metal-ore particulate.
 15. The compositeparticle of claim 14, wherein the metal dust comprises a metal of themetal-ore particulate.
 16. The method of making iron comprising:smelting a mixture of iron ore, coke, and a plurality of compositeparticles according to claim 6; and cooling the molten iron.
 17. Amethod of recycling iron oxide waste dust from a steel- or iron-makingoperation, the method comprising: mixing the iron oxide dust with amineral clay binder to form a coating; applying the coating as a layeron a limestone or dolomite aggregate core to form a composite particle;and re-smelting the composite particle with ore and coke.
 18. A methodof smelting a metal alloy comprising: smelting a mixture of at least onemetal ore and a plurality of composite particles according to claim 1,the metal dust of the composite particle being a component of the metalalloy; and cooling the molten metal.